Filament-plate voltage system



March 13, 1951 Q N FILAMENT PLATE; VOLTAGE SYSTEM Filed Oct. 31, 1947 R an N/ mm we AIL FEED Patented Mar. 13, 1951 FILAMENT-PLATE VOLTAGE SYSTEM Alfred 0. C. Nier, Minneapolis, Minn., assignor t Regents of the University of Minnesota, Minneapolis, Minn., a corporation of Minnesota Application October 31, 1947, Serial No. 783,432

9 Claims.

In mass spectrometers and certain other instruments it is important in the satisfactory operation to provide a source of constant electron emission and in many instances also to provide a constant acceleration and trap potentials for the emitted electrons. The power supply systems heretofore available for such purposes have not been completely satisfactory in that the desired constancy of emission and potential has not been achieved, nor have power supplies heretofore available provided adequate safeguards against breaking of vacuum in the enclosing vessel and have not afforded the needed and desirable facilities for adjustment over wide ranges of emissivity.

It is an object of the present invention to provide an improved power supply of regulated character capable of providing regulated plate and filament voltages for achieving constancy of emission of electrons in mass spectrometer tubes and kindred instruments.

It is also an object of the invention to provide an improved power supply of the aforesaid character wherein adequate safeguards are provided against malfunctioning in the event loss of vacuum should occur in the instrument to which it is connected.

It is also an object of the invention to provide an improved power supply for mass spectrometer tubes affording easily regulated variations in filament and plate supply, while yet maintaining fixed proportionality between certain voltages supplied, as for example the voltage supply for the trap and shield of the mass spectrometer tube.

Other and further objects of the invention are those inherent in the apparatus herein illustrated, described and claimed.

The apparatus is illustrated in the drawing which shows a wiring diagram of an exemplary power supply system of the present invention.

Throughout the drawings corresponding numerals refer to the same parts.

Referring to the drawings, Figure 1, the power supply system includes the supply lines L1 and L2 which are supplied with alternating current at standard voltages and frequencies, such as 110- volt alternating current supply. Line L2 includes the fuse I and a manually operated control switch l2 for turning the system on and oif. Line L2 continues to one terminal of the primary l4 of transformer I5; Line L1 is connected to the opposite terminal of the winding M. The secondary l6 of the transformer l5 supplies the power supply bus bars I1 and I8. To the bus bars and I8 there is connected the primary winding 28 of a transformer 2|, the secondary 22 of which supplies the filaments of the indirectly heated cathodes of all tubes in the system for which filament sup-ply voltage is not otherwise shown in the drawings. The bus bars H and I8 are also connected to the primary winding of a power pack shown over bracket 45, which includes supply transformer 25.

The transformer 25 includes a filament secondary 26 which is connected through lines 21, 28 and 29 to the cathode 3|! of a full-wave rectifier tube generally designated 3|. The rectifier tube anodes 32 and 34 are connected by lines 35 and 36, respectively, to the terminals of the secondary winding 31 of transformer 25. The mid tap 38 of the transformer winding 31 is connected to line 49 which constitutes the negative supply line of the power pack, including transformer 25 and rectifier 3|. The output of the rectifier which appears on l nes 21 and 40, respectively, is filtered through a filter network including an inductance i! and two condensers 42 and 43, and the positive direct current supply voltage which is thus supplied to line 44 (positive), and line 40 (negative) is comparatively free from any ripple or alternating current component.

Under the bracket 46 is a transformer and thermionic tube network, the function of which is to supply a controlled filament voltage to the filament terminals 41 and 48 which are connected directly to the filament of the mass spectrometer or similar apparatus with which the supply system is intended to cooperate. A fragmentary schematic view of a portion of the ion source of an isotope mass spectrometer is shown at the right in Figure 1. In this View the filament which is connected to terminal 41 and 48 is insulated from and is housed in one compartment of a shield box which is connected to terminal S. The trap is connected to terminal T. The apparatus 46 includes a transformer generally designated 50 having a primary winding 5|, one terminal of which is connected to the bus bar I8 and the other terminal connected through variable resistors 52 and 53 and through the contacts 54 of a control relay |50 to the opposite bus bar IT. The control relay I50 is of the type which closes its contacts 54 when the operating coil I48 of the relay is energized and is a safety device. Its function will be explained in greater detail hereinafter. During the operation of the power system the contacts of relay 54 are closed and the supply voltage across bus bars l1 and I8 is thus 3 applied to the series network including transformer winding 5| and resistors 52 and 53.

The transformer 59 includes a low voltage filament voltage secondary 55, the terminals of which are connected through the lines 58 and 59 through the filament supply terminals 4]. and 48, respectively. The central tap t the secondary 56 is connected to line 60.

The transformer 59 also includes a comparatively higher voltage secondary winding 6|, the terminals of which are connected through lines 62 and 53 to the anodes 64 and 550i the grid; controlled thermionic tube generallydesignated 66. Tube 66 includes indirectly heatedcathodes. 6i and 58 which are connected to line 69 that is in turn connected to the center tap I ofthesecondary winding 6|. Tube 66 includes alsothe control grids II for each cathode-anode system, he. grids bein con e t d t gether so as o I at the same voltage.

The tube 55 serves to load thetransf ormer. secondary 6,! to a varying degree, depending upon thejvoltage which is applied tothe grids TI. The voltageso applied tothe grid II is the regulating voltage of the system and the manner in which. this regulating voltage is supplied will be later described in detail. As, the voltage on grid 7| varies, the loading on the tube 65 is likewise varied, and, hence draws more, or less. current from, the secondary winding 6| and accordingly variablyloads the transformer primary Inasmuch asthe transformer Winding 5| is supplied froml bus bars I1 and I8; through a resistor networl; including resistors 52 and 5 3 in series, the ary n oadc e flowin th oug h a y Min accordance with, the varying was on the secondary 9 I causes a varia i vo tage C thelterminals of the primary winding 5|. These variations. are. manifested also upon, the. Voltage upplied. y e filament, ndi s as d h r f lliei as the. secondary 5| is loaded in varying amcunt, the voltage on winding 59 will likewise vary, and the massspectrometer or the like. filaie t whi hgis, suppl db rmi ls 1 an 8.

will be heated varying amounts, depending in nal. aadvs sun the vo ag u l d ri II; i

In a ectrome er. nstrum t it s r ired o re ula efihe' mis ion r the. am n Thus, a filament connected to the terminals 48 d. alndf h ebv he t i it le t o -iidv tf lds i e qw tml he mouo to,

regulate the constancy of emission from such a filament. The heating of the filament, per se, is unimportant except aslit has a bearing upon the emission of electrons therefrom. In order to provide for regulation of the amount of emission from the filaments supplied by terminals 4'1 and i8=andalso to provide for constancy of such electron emission, there is provided a regulating network shown over the bracket I2. The network is supplied by lines 44 (positive) and 40 (negative). a regulating resistor I4 and thence line I5 to junctions I5 and I1; LineAO extends likewise to junctions I8 and I9.

Between junctions I6 and I8 there is'a series circuitincluding a fixed resistor-89, variable re-. sistor 3|, junction 82, voltage regulator glows.

tube'84, junction 85, voltage-regulator glow-tube 89, junction 81, voltage regulator glow-tube 88, junction 89, fixed resistor 99 and variable re-. sistor 9|. are connected together, as indicated by the common control line 92, and in such a manner that Linev 44, it being noted, extends through The controls of resistors 8| and 9| 4 as the control 92 is moved to decrease resistor 8|, the resistor 9| is simultaneously increased by a corresponding amount and vice versa. It may be noted, however, that even though variable resister 8| should be reduced to zero, there is still afixed resistance 89 between junctions I9 and 92 and that likewise even though variable resistance 9| is regulated to the zero position, there is still a fixed resistance 90 between junctions I8 and 89.

Across junctions TI and I9 there is a series circuit parallel to that connected across junctions I6 and I8. The latter circuit includes a voltage regulator glow-tube 93, junction 94, voltage regulator glow-tubee'd junction 96, voltage regulator glow-tube 91 and thence to junction I9. The three tubes 93, 95' and 91 thus divide the voltage acrossijunctions TI and 1'9 constantly and in a manner determined by the voltage drop across the individual tubes, and junctions 99 and 95 whichaccordingly remain at fixed potentials in respect to junctions 'I-I and I9, serve to supply thetrap and shield voltages of the mass spectrometer tube,the filament of which is supplied by terminals 41 and 48. Thus, line 93 connects junction 96- to the shield voltage terminal S. Junction 94, is connected to switch terminal 99 and through a. resistance I90 to the cooperating switch terminal- Ill-I andthence through a fixed resistance I92 to the trap voltage supply terminal T whichis connected tothe electron trap of the mass spectrometer tube, the filament of which is supplied by terminals Hand 48.

Opposite the bracket IM there is shown a meteringsystem including the microammeter M which isconnected-through resistance I05 to the blade terminals, IBB and ID? of; a double pole double throw switch. Blade IIIl-is connected to theterminal I95 and blade III to the terminal Iii-I7 anda condenser II2- is connected across the twoterminalsltlli and lil'i' so asto by-pass any momentary surges which might be harmful to themeter M, The switch blades Hi3 and III are adapted to be closed'on the terminals 99 and IOI, respectivelyandin this, position the meter M reads the current flowing in the trap circuit of the mass spectrometer tube connected to terminal T; The switch blades IIiland I I are also adapted to bemoved into contact with terminals H4 and] I5,which are shunted'bya resistor I I6. Line fiily which is connected to the center of the filamerit supply winding 55, is connected to switch contact |I l andswitchcontact I I5 is connected to line II'I; This circuit (which will be later explained in gteater detail) supplies the emission current constituted by theelectrons emitted by the mass spectrometer or other instrument filament connected to terminals 41 and 48. Hencawhen the switch bladesIIt and HI are closed upon contacts I|4.and H5, respectively, themicroammeter M- reads the emission current.

Line III; which supplies the emission current, is connectedtojunction |I3 on the lead of control grid I26 (tubew I25) and thence through fixed resistor ||8 and,variable resistor II9 to junction 89, From junction 8? a line extends through junction I29 and thence through line. |2| to junction |22 and to the cathode I24 of tube I25. Tube I 2 5,incl udesa controigridIN and screen grids I21 and I28, the latterbeing Connected to junction I22 and, is .hence maintained at cathode potential, Grid I21 is-connectedto-junction I29 whichis, connected thrcl ghline I30 to junction 8 5 and,from junction I29 line -|3I extends to the grid II of the loading tube 66. The anode I32 of the tube I25 is connected to junction I33 and thence through fixed resistor I34 to junction 82. Junction I33 is also connected through line ,69 to the cathodes 61 and 68 of the loading tube 66. The control grid I26 of the tube I25 is connected to junction 3 and thence through a condenser I35 to junction I28 (hence to junction 81).

Opposite the bracket I36 is a vacuum break safety control circuitincluding terimnals|31 and I38 which are connected to a switch that is closed when vacuum is maintained in the system but which opens when the vacuum is broken, i. e. when the pressure increases in the mass spectrometer tube or other apparatus supplied by the filament terminals 41 and 48, trap terminals T and shield voltage supply terminal S. Terminal I31 is connected through junction I48 and line I4| to supply line L1. The apparatus within the dotted line I42 is a double contact relay having pairs of contacts I44 and I45 which are open when the coil I46 of the relay is deenergized. Contacts I45 are shunted by push-button contact I41 and contact I44 is in series circuit with the coil I48 of the relay I58 having contacts 54 which are maintained closed when coil I48 is energized. When the mass spectrometer or other tube which is supplied by the instant system is put in operation the vacuum is initially pumped in the tube and through a suitable vacuum operated switch the circuit is closed across I31 and I38 when a sufficient vacuum is maintained. Push button I41 is then closed and this establishes the circuit from line L1, through lines |4| and through the then closed circuit across terminals I31 and I38 to coil I46, thence through push button I41 to line L2. Coil I46 being thus energized actuates its contacts I44 and I45. The latter serves to maintain a circuit through the winding I46 and is a self-holding circuit. The closure of contacts I44 energizes the coil I48 of relay I58, and this serves to close contacts 54 of relay I50 and thereby establishes the circuit from bus bar I1 through contacts 54, resistances 52 and 53 to winding 5| of the transformer 58 which supplies the filament voltage to terminals 41 and 48.

All of the tubes 84, 86, 88, 93, 95 and 91 are of the voltage regulator or glow type which maintain a constant voltage across their respective terminals, regardless of the amount of current flowing through them, within wide limits. The tubes 93, 95 and 91 divide the voltage which is supplied across positive line 15 and negative line 8| and, 98,9I; Hence, the filament potential is maintained at the voltage of junction 89. Since resistors 8| and 9| are connected together in a put-and take arrangement by the common control 92 sothat as resistor 8| is decreased, resistor 9| is increased and vice versa, it follows that by operating the gang control 92, the voltage at junction 89 may be regulated from a minimum or most negative voltage which occurs when resistance 9| is reduced to zero and resistance 8| is at a maximum, thence through a range of more positive potentials to a maximum potential which occurs when resistance 9| is at a maximum and resistance 8| is at a minimum. In this manner the voltage of filament connected to terminals 41 and 48 is regulated with reference to the voltage of terminal S, which is connected to the shield of the mass spectrometer tube and is the voltage of reference. It may be noted that the value of the currents flowing normally through the circuit from junction 16 to junction 18 is much greater than the emission current from the filament connected to terminals 41 and 48 and hence in the emission control analysis hereinafter given the voltage drop occasioned by the emission current flowing through resistor 99 and 9| is neglected.

The electron stream constituting the emission fiow from the filament connected to terminals 41 and 48 begins at the filament 30 of tube 3| and passes from the filament to one or the other of .the plates 32 and 34, thence through the winding 31 to mid-tap 38 and by way of line 40 to terminal 18, thence through resistors 9| and 90 to terminal 89 and through resistors II9 and H8, grid junction II3, line I I1, resistor M6 to line 60, thence through the winding 56 and through lines 58 or 59 to the filament. The electron flow returns from the electron trap of the mass spectrometer which constitutes one of the plates of that tube and is connected to the terminal T. The flow returns then through the resistors I82 and I80, junction 94, tube 93, junction 11 and then by way of line 15 through resistor 14 and line 44, in ductance 4| and line 28 to the filament 38 of tube 3 I.

If it is assumed that the emission of electrons from the filament connected to terminals 41 and 40. For purposes of analysis the voltage supplied at junction 66 through line 98 to the shield voltage tap S may be considered as the voltage of reference in the instrument. Voltage divider tube 91 is, for example, of the 150-volt type and hence junction 19 and line 46 are at minus 150 volts (150 volts below the voltage of shield tap S). Tubes 93 and 95 are each of the I5-volt type and hence the trap voltage supplied at terminal T is plus '75 ('75 volts above the shield voltage at shield tap S), and the voltage at terminal 11 is plus 150 volts or 150 volts above that at the shield voltage tap S.

The voltage divider circuit through resistor 80,

'8I, tubes 84, 86 and 88 and resistor 98and 9| establishes the voltage of the filament connected to terminals 41 and 48 in respect to'the shield voltage tap S. Thus, the mid-point of winding 56 supplying the filament supply terminals 41 and 48 is connected through line 68, resistor H6, and line H1 and resistors H8 and M9 to junction 89 immediately below voltage divider tube -88'-.- The voltage at junction 89 is determined by the voltage dividing circuit which includes resistors-88;

48 decreases, the resistance drop through resistors H8 and H9 will accordingly likewise decrease and junction ||3 tends to become more negative, thus decreasing the conducticity of tube I25. There is a parallel jcircuit around tubes 84 and 86 from junction 81 through line I2I, to cathode I24 of tube I25 and thence to the anode I32, junction I33 and resistor I 34 to junction 82. The potential of junction I33 in this parallel circuit is determined by the relative impedance of resistor I34 and tube I25. Hence, when the tube becomes less conductive the effective, internal resistance of the tube I25 is in effect increased and the potential of junction I33 more nearly approaches the potential of 82, or stated another way the potential of junction I33 becomes more positive. The grids 1| of tube 66 are maintained at a constant potential by virtue of the connection through lines |3| and I30 to junction 85 on the voltage divider circuit between junctions 16 and 18. It may be noted parenthetically that the potential at junction 85 is fixed by variation of control 92 does not effect the con trol of emmissivity of the filament connected to terminals-41 and 48. The cathodes 61 and 68 of tu 5 are however, sub ct to the varying t eme a a tion. or bei nn e t eme through line '69. Therefore, as junction 133 becomes more positive, as previously described,

this makes thev Cathode 61 and 68 of tube 66 relatively positive which in efiect makes the grid 1 l r elatively more negative in respectto the cathode, and tube 66 becomes less conductive. When this occurs a lesser current flows in the cathode-anode circuit of tube 66 and a lesser loading of the transformer secondary winding BI occurs with consequent decreased loading on the primary winding 5|. The decreased load on the primary winding 5| has the efiect of decreasing the resistance drop through resistors 52 and 53. Hence, the portionor the potential across bus bars I! and IQ which is effectively applied to the winding 51 is likewise increased, and consequently there an increased voltage induced in secondary 56 which supplies the filament of the mass spectrumear tube. As the applied voltage to the filamerit is thus increased, its temperature is raised seems emission is increased until balanced conditions are re-established.

An' increase inemission of the filament supplied by terminals 41 and 48 has a reverse effect as compared to that just explained and the voltage supplied to terminals is reduced until balance is again l e-established.

The initial control voltage which accomplishes the aforesaid regulating function is the resistance drop across resistors H8 and H 9 which determines the voltage of grid I26 with reference to the voltage of the cathode I24. As the emission current to be regulated flowing through resist ances 8 and H9 increases, the voltage of grid junction 1 timore-nearly approaches the cathode reference voltage at line I24 and junction 81. Tube 88 maintains a constant difference in potential between junctions 8'! and 89.

Fixed resistors 88 and 90 are included in the bridge circuit between junctions 76 and 1-8 to prevent r un -away operation of the regulator. These resistors insure that the voltagept the filament connected to terminals 41 and 48- will always :be at least a minimum amount below the shield voltage S and trap voltage T, regardless of the extreme operation of the put-and-take gang iofresistors-il I and 9-1. This insures against a condition inwhich the regulating action of the system (portions 46 and 12) wouldtend to supply an evereincreasing voltage to the filament supply terminals 41 and d8-wherethe emission decreased or was absent altogether due to lack of proper potential gradient to the trap (connected to 5 terminal T) and shield (connected to terminals) Regulation of emissivity of the filament supplied by terminals 41 and 48 can be manually regulated by varying resistance H 9- s ince a change in the resistance of its circuit is equivalent to a change in emission current therethrough in producing the regulatory IR drop therethrough. Resistors 52 and 53 permit adjustment to insure that the amplifier tube .56 operates on. a favorable part of its characteristic curve, and .in this manner. permit "the sensitivity of the instrument to be. varied Variable, resistance It provides .a ready means of controlling the, current through tubes 93, 95 and :91; tosaife limits since these tubes are connected directly across lines :1 and 4,0.

a a pa en Widely f e e mbod me ts th s in entio a e ma w th u epartin rom the s ir t a s op ther o t is t he a esstqed i at do? aetl m tmrseli t the sas ifls emb diments he e n c pt s sensed by wane da ea r am s:

P 7 g ow r p y tem f l m s ect qmeters and the lilge thermionic tubes having a lissts filame n a P at f r r in n collecting the electrons emitted therefrom, Varivoltage. means connected to said filament,

- variable plate voltage supply means connected oa- I r e ters a con e ed t er e mi l en qu to said plate and filament, means responsive to the electron emission of the filament connected to the'voltage supply means forincreasing and decreasing the voltage ofsaidvariablevolta emeans connected to said filament in response to variat ions in emission from said filament, said plate voltage supply means including a pair of supply li s. between which a relatively constant voltage m i t ned an a series o re sta c was said supply lines one of which resistances connec d d acent one en of t ser es nd the last oi which resistances at the other end are var a e a onnec ed to e h so at a one increased the other is correspondingly decreased, said filament and plate being connected to an intermediate point on said series and to one oi the supply lines respectively.

2 The apparatus of claim 1 further characteriaed in that it includes a second series comprieed of voltage regulator elements between said supply lines, said filament and plate being connected to intermediate points, respectively, of said, series oi resistances and said second series comprised ofvoltage regulator elements.

3. In a power supply system for mass spectrometer and the like thermionic tubes having a heated filament and a plate for accelerating and oolieotingthe electrons emitted therefrom, variable voltage means connected to said filament, plate voltage supply means connected to said plate and filament, means responsive to the electron emission of the filament connected to the voltage supply means for increasing the voltage of said variable voll i e means when the electron emission decreases and for decreasing the voltage when the emission increases, said plate voltage supply means including a pair of supply lines "between which a relatively constant voltage is maintained, and a series resistance network connected acrosssaid supply lines forming a voltage divider circuit which establishes the voltage of said filament in respect to said plate of the thermionic tubes including a first variable resister, a plurality of voltage regulator tubes and a second variable resistorin the order named, said means responsive to the electron emission of the filament including a branch circuit having a resistance connected to an intermediate voltage 2 1 2 a erie is an e wq k an t said variable voltage supply means.

4. The apparatus of claim 3 further characterized that said branch circuit resistance is a able i 5. The apparatus of claim 3 inr tl er characterized in that the first and second variable ree eei el acet tes P-dec e eon the. oth r i ncre sedt T e a par us o Claim i b r h racte d tha h Series s s anc lu e a rst ix d s ta ce con ected o sai fi st; ariab e resist r and a. econd ixer r s stance. nne te o, aid se ondvariab e res stor.

-'I.-. h a paratus '.o cl m 3: f rther cha s ensediin that-sai p ate scpnp cted be ween 10 REFERENCES CITED The following references are of record in the file of this patent:

5 UNITED STATES PATENTS Number Name Date 1,406,328 Atherton Feb. 14, 1922 1,683,194 Kearsley Sept. 4, 1928 2,048,203 Spencer July 21, 1936 10 2,319,378 Weisglass May 18, 1943 

